1. Field of the Invention
The invention relates to the technical field of color signal interpolation and, more particularly, to a color signal interpolation system and method for reconstructing green color.
2. Description of Related Art
A color image processing system essentially includes an image capture unit, an image reconstruction and processing unit, an image display and an image compression unit. The image capture unit includes an image sensor and a color filter array (CFA). FIG. 1 is a schematic diagram of a Bayer CFA and associated interpolation operations. As shown in FIG. 1, the frame is arranged in a form of interlaced GR-contained row and BG-contained row, where R, G and B are the three primary colors: green, red and blue (RGB). Each photosite in the CFA can have only one of RGB. The image reconstruction and processing unit thus uses an interpolation to reconstruct missing colors for each photosite, which fills up the respective green, red and blue planes.
In addition, the image sensor has the pixel crosstalk effect in which, when a pixel is illuminated by a light, charge generation and signal transmission will diffuse to the neighboring pixels due to the semiconductor process in pixel layout and production. In accordance with the observations and experiences, the horizontal crosstalk effect is stronger than the vertical crosstalk effect. For the example of Bayer color filter array, red and blue pixels present the crosstalk on the respective left and right green pixels. Due to the pixel crosstalk effect, the left and right green pixels relative to a red pixel have different outputs from those relative to a blue one. In this case, the pixel value of a green photosite presents an error component. Thus, the pixel crosstalk effect can be seen obviously in a flat area when an interpolation is used to reconstruct each pixel's red, green and blue values because of the result of error component.
To overcome this problem, U.S. Pat. No. 6,727,945 granted to Jaspers for a “Color signal interpolation” has disclosed that a difference of green photosites at different rows is compared to a threshold to accordingly determine if a corresponding photosite locates on an edge area, thereby selecting one from an original green value of the photosite, a interpolation value, or an average value for the corresponding photosite. However, the threshold is computed with pixels (on the RGB domain) captured by the image sensor, which encounters the problems of lower representative, easy to cause a resolution reduction, and hard to improve the crosstalk effect caused by a green error. Therefore, it is desirable to provide an improved color signal interpolation system and method to mitigate and/or obviate the aforementioned problems.